1. Field of the Invention
This invention relates to composite metal articles, and paticularly but not exclusively to ring carriers for pistons, blanks therefore, pistons incorporating such ring carriers, valve seats and cylinder heads incorporating valve seats.
2. Description of the Prior Art
It is well known to provide a piston with a ring carrier of a more wear resistant material than the body of the piston, a groove being machined in the ring carrier to receive the piston ring. For example aluminum alloy pistons for use in diesel engines may be provided with a ring carrier of a special cast iron, the ring carrier being placed in the mold, and the aluminum alloy being cast around it during manufacture of the piston. The ring groove is machined in the ring carrier during machining of the casting.
It is also well known that there are difficulties in obtaining a reliable bond between the ring carrier and the body of the piston, especially where the ring carrier is of a ferrous material and the body is of aluminum alloy. British Patent No. 892,770 (Hepworth & Grandage Limited) describes and claims a method of casting aluminum or an aluminum alloy on to a ferrous metal part which consists in spraying a coating of molybdenum on the surface of the ferrous metal part on to which the aluminum or aluminum alloy is to be cast, spraying a coating of aluminum or an aluminum alloy on to said molybdenum coating, preheating the coated part, and then casting aluminum or an aluminum alloy on to the sprayed surface.
British Patent No. 1,161,663 (Wellworthy Limited) describes and claims a process of producing a composite metal article, comprising applying a layer of tin to a sintered ferrous metal component, and casting a metal against the coated sintered component.
British Patent No. 1,164,289 (Wellworthy Limited) describes and claims a process of producing a composite metal article which comprises coating a ferrous metal component or a sintered ferrous or non-ferrous component with a spray deposit of molbdenum, coating the molybdenum with a layer of tin, and then casting a non-ferrous metal against the coated metal component.
In these cases, a surface layer of molybdenum, or of tin, or of molybdenum and tin, is essential, in order to effect a bond between the ferrous metal and the non-ferrous metal.